Transducer



NOV. 23, 1948. w,. ASHTON 2,454,496

TRANSDUCER Filed April 9, 1947 wmwlyww 1/ jnaenzar JOWMW/SMW @QMJlW' Patented Nov. 23, 1948 TRANS DUGER Howard W. Ashton, South Ardmore, Pa., assignor to 0. W. Storey & Associates, Chicago, 11]., a

partnership Application April 9, 1947, Serial No. 740,419

7 Claims. 1

This invention relates to a transducer utilizing a capillary electrometer as the transducer element. In Patent 2316,5378 to Burgess, a capillary electrometer-type of transducer is disclosed. The invention herein is an improvement upon the invention disclosed and claimed in the Burgess patent and provides a simple, compact and efflcient structure.

As disclosed in said Burgess patent, a capillary electrometer-type transducer comprises an insulating tube of glass or the like having a capillary channel within which mercury and an electrolyte, such as dilute sulphuric acid, meet forming at least one interface. Instead of mercury, gallium may be used and, instead of sulphuric acid, other solutions, organic or inorganic, may be used.

In order to provide efiective transducer action, suitable means are necessary for transmitting energy to or from the capillary electrometer, depending upon the direction of energy conversion. The transfer of electrical energy from within the capillary system is comparatively simple and may, for example, be accomplished by the use. of wire leads in conducting relation to the interface-forming liquids. The conduction of vibratory energy to or from the capillary system involves substantial difliculties. The invention addresses itself to means for providing a path. for transfer of energy between the interior of the capillary electrometer and the exterior thereof. In general, the energy transfer path permits the fiow of energy in either direction so that the transducer may be used either to convert electrical energy into mechanical energy or vice versa. While certain embodiments of the invention may be more advantageously used for conversion of energy in one direction, such as from mechanical energy to electrical energy, it will be understood, however, that the structures in general are reversible as far as operation is concerned.

A capillary electrometer has been found to be sensitive to liquid movement in connection with elastic deformation of an end wall-forming part of the enclosure for the interface-forming liquids. In order to utilize this mode of operation, this invention provides structures having weakened flexing portions to promote transfer of energy between the interior and exterior of the capillary system.

A more complete explanation of the principles of operation of structures embodying this invention is more conveniently given in connection with a description of the invention. The invention will, therefore, be described in connection with 2 the drawings wherein Figure 1 is a sectional elevation of a structure embodying the'invention. Figure 2 is a sectional elevation of a modified form of structure embodying the invention. Figure 2A is a detail of the stylus mounting. Figure 3 is a sectional view of a modification of the structure shown in Figure 1. Figures 4 and 5 are sectional views of still further modifications.

Referring now to Figure 1, glass tube in has capillary channel ll therein terminating in enlarged regions or chambers l2 and I3. Region I3 is connected by capillary bore H to gas chamber l5. Tube ID has sealed end IS in which is disposed wire lead l1. Wire lead I! is sealed at l6 and extends through chamber l5. Lead I! has portion iii 'in coiled form extending through capillary l4 and into region l3. Portion l8 of the wire may be of platinum or other conductor inert to the interface-forming liquids- Wire l1 itself may be of cheaper material, such as borated copper, and may be heavy enough to permit handling.

Disposed within enlarged regions l2 and I3 are bodies of mercury. Within capillary II are globules of mercury and other interface-forming electrolyte, such as sulphuric acid diluted to a concentration of the order of between 10 and 40%. Inasmuch as the requirements for liquids forming a capillary electrometer system are well known, it is unnecessary to go into detail. Chamber l5 has gas or air therein at any desired pressure. Inasmuch as the gas pressure in chamber i5 provides compliance to the system, the characteristics of the system may be controlled by choice of gas pressure.

Capillary bore ll may have a diameter of between about five and about one hundred microns (.005 mm. to .1 mm.) and may have any desired length, such as, for example, 10 mm.-although other bore diameters and lengths maybe used. Enlarged regions i2 and I3 may themselves be of capillary dimensions, such as about one mm. in diameter and may have a length of about 5 mm. It is understood that capillary bore H and enlarged regions l2 and I3 are circular although other cross-sectional configurations may be used. In general, region or chamber l3 should have as small a volume as possible consistent with good construction.

Sealed in the wall of glass tube in is lead 20 having portion 2! extending within region i2.

If' desired, auxiliary glass portion 22 may be utilized for forming chamber 23 within which the junction of wire 20 and tip 2| may be disposed.

25. Annular flexing region 28, where the two portions unite, is thin and has substantial flexibility. It'is preferred to have diaphragm 21 quite rigid,

although this may be thin and flexible if desired.

Region within annular portion 28 and' between diaphragm 21 and portion 25 is fllled with liquid, such as mercury. If desired, a gas chamber similar to IE may be provided in com tion with regions I2 or 30. It is understood at the capillary passage leading to a gas chamber, such as passage H for example, are fine enough to prevent liquid, such as mercury, from passing through.

The structure so far described in Figure 1 may be used as a capillary microphone. Sound waves in air or in liquid impinging on the outside of diaphragm 21 will cause displacement of the interfaces in capillary bore H and result in potentials being generated by the electrometer. It is not necessary that portion 25 flare as much as indicated in the drawing. It is desirable to have diaphragm 21 and flaring portion 25 spaced quite close to reduce the volume of region 30. It is only necessary that diaphragm 21 have sufficient space within which to vibrate freely without touching flaring portion 25.

It is evident that, in the construction shown in Figure 1', a substantially incompressible connection is provided between diaphragm or piston 21 and the interfaces within capillary bore II. This is true even though small bubbles of gas may be permitted to remain within the system. In view of the nature of this connection and the fact that the energy is transmitted by compressional waves in the liquid, it is clear that the liquid path itself need not necessarily be straight. It is desirable to so design the liquid path that interference and diffraction effects are avoided. However, it is evident that the comparatively narrow liquid path provided by regions i2 or 13 in Figure 1 may be bent out of a straight line without having substantial effect on the transmission characteristics of the liquid path.

Referring, therefore, to Figure 2, a modified construction is shown wherein glass tube I0 has portion bent as shown to form a substantial right angle. This is exemplary and the amount of bend may be set to any desired value. Beyond bend 35, glass tube ID has portion 36 terminating in annular flexing region 31. Region 31 may be constructed generally along the same lines as the corresponding part in Figure 1 with a comparatively heavy fiaringportion 38. This construction, however, differs from Figure 1 in that part 39 of the annular portion is reenforced. Heavy wall portion 40 is provided. Wall portion 40 carries rod 4| of glass or other suitable material. Flat spring 42 extends from rod 4| and has attached thereto stylus tip 43. Stylus tip 43 may be of the type used in phonograph work and may conveniently be formed of a sapphire or other jewel or of hard metal, such as carballoy, tool steel, or the like. Spring 42 is flexible for vertical stylus movement but quite rigid for lateral stylus movement.

In order to protect the transducer or pick-up from damage due to careless handling, hood 45 may be disposed around the same. Hood may be of plastic or sheet metal or any other suitable material and has a generally conical shape.

,, The hood may be formed in two portions and may be cemented around part 36 of the glass tube. Hood 45 has tapered portion 46 which approaches stylus tip 43 and provides just enough clearance for proper stylus operation. In the event that the structure is dropped upon the stylus tip, weakened region 31 will yield sufficiently to permit the tapered portion of the hood to take up the shock and prevent excessive flexure of the glass.

The entire pick-up may be rigidly supported 'by suitable 'means clamping the body of tube Ill and may be disposed in a tone'arm in a conventional manner.

In the transducer shown in Figure 2, wall 40 is adapted to be tilted rather'than moved lik'e'a piston,

with respect to reenforced portion 39 and result in transducer action. This is due to the fact that reinforcement 39 does not extend all the way around annular region 31 but forms only a small part thereof. It is, thus, evident that reeni'orced portion 39 of annular region 31 should be properly oriented. Vertical movement 'of the shape of a conical surface. Portion .50 has thin' flexing region 5|, and this region supports concave vibratory portion 52. Conical portion 50 may have a shape similar to a portion of a spherical surface rather than a cone. Such a construction may be formed from a. hollow glass sphere by softening the glass and pressing the same against a suitable die member.

In Figure 4, a, somewhat modified construction is shown wherein flaring portion 53 has flexing portion 54 and has concave portion 55 of the shape shown. As clearly indicated in the drawing, this concave vibratory portion has the general shape of a saucer.

In Figure 5, a, construction similar to Figure 4' is shown but differing therefrom in that lead 51 passes through the concave vibratory portion 55'. Lead 51 may be made rigid enough to function not only as an electric conductor but also as a mechanical element. Thus, forces transverse to lead 51 or along the length of lead 51 may be provided for operating on diaphragm portion 55. It is understood that the forms shown in Figures 3 to 5, inclusive, are maintained rigidly in position by suitable means clamping the body of the transducer. It is also possible to rely upon inertia for maintaining the body of the transducer in more or less fixed position.

What is claimed is:

1. A transducer comprising a tubular insulating member having a capillary bore and enlarged regions at opposite ends of said bore, capillary electrometer interface-forming liquids within said member and forming at least one interface within said bore, conducting liquids in said regions, said tubular member having a flaring portion at one end thereof and having an end wall sealing said tubular member at the flared portion, said flaring portion forming part of one of said enlarged reas in Figure 1. Transverse move-' ment of stylus tip 43 will cause tilting of wall 40' gions and having a weakened, annular flexing -zon'e, and leads to the liquids on opposite sides of the capillary.

2. The structure according to claim 1 wherein said insulating member is sealed and is formed of glass. I

3. The structure according to claim 1 wherein 7. A transducer comprising a sealed tubular glass member having a capillary bore at an intermediate point thereof and enlarged regions at opleast one interface within said bore, mercury in said enlarged regions for providing electricailyconducting paths to said interface-forming liquids, said tubular member having a flared portion at one end thereof and having an end wall sealing said flared portion with a weakened annular flexing zone at said flared portion for permitting vibration of said end wall, said end wall and flared portion forming part of one of the liquid-filled rgions, leads to the liquids in said two regions, said end wall being adapted to vibrate during energy conversion.

. 20 posite ends of said .bore, mercury and sulphuric acid within' said capillary bore and forming at Number HOWARD W. ASHTON.

- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,738,988 DeForest Dec. 20, 1929 

